Fluid regulators are used in a wide variety of environments for both commercial and industrial applications. For example, fluid regulators find use in pipeline systems, chemical plants, and building environmental systems. Regardless of environment or application, most modern fluid regulators are controlled by some type of logic-driven controller, whether located with or remote from the fluid regulator. A controller allows a fluid regulator to be controlled in an intelligent manner to achieve one or more desired effects (e.g., flow rate, pressure, temperature, level, energy efficiency, etc.).
A common type of fluid regulator controller operates by pneumatic techniques. This type of controller often receives an external air supply and manipulates the air supply in response to electronic commands to actuate the fluid regulator appropriately. Thus, a pneumatic controller is often said to include an electric-to-pressure converter. Depending on the fluid regulator to be actuated, a pneumatic fluid regulator controller may also include a second pneumatic component. This second stage of the controller may amplify the pressure and/or volumetric flow rate of the output of the electric-to-pressure converter. Common devices for accomplishing this include a spool valve and a pneumatic relay.
One type of electric-to-pressure converter includes an electric coil and a magnetic core that move relative to each other. The movement occurs in response to a command signal, which changes the current in the coil and energizes the magnetic core, and adjusts the output pressure. In one arrangement, the magnetic core includes a hinged flapper that moves relative to the body of the core and the electric coil to adjust the output pressure. This arrangement, however, may have significant hysteresis, deadband, and non-linearity, which makes it difficult to accurately control. In another arrangement, the electric coil moves relative to the magnetic core, which provides low hysteresis and good linearity for the converter. Unfortunately, the second arrangement is expensive to construct due to the required tolerances and can be unreliable due to exposure of the fine wire that is required.